Towards Predictive Rendering in Virtual Reality

The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation

Sandwich core periodic cell topology effects

Les panneaux composites sandwich possédant une âme nid d'abeille permettent de disposer à la fois de propriétés statiques hors plan intéressantes (en raison de leur rigidité équivalente élevée) et de caractéristiques de masses faibles. Pour cette raison, ils sont largement utilisés dans les industries aérospatiale, automobile et navale. Les environnements dans lesquels ces matériaux sont utilisés mettent en jeu des efforts dans des gammes de fréquences larges. Si un rapport rigidité / masse élevé est profitable dans le domaine des basses fréquences, il conduit généralement à des comportements vibratoires et acoustiques médiocres lorsque la fréquence d’excitation augmente. La question abordée dans ce travail peut être formulée comme : comment les concepts périodiques peuvent-ils améliorer les signatures vibroacoustiques large bande et les performances de ces structures ? La plupart des solutions vibroacoustiques sont limitées en terme de bande de fréquences d’efficacité, et induisent généralement un ajout de masse. La prise en compte de règles de conception vibroacoustiques à un stade précoce du développement du produit est l'un des principaux objectifs de recherche en vue d’améliorer leurs performances et permettrait de concevoir des structures accordées sans aucune intervention ultérieure ou augmentation de masse. Ce travail se concentre donc sur l'étude des topologies de base de panneaux sandwich existants et a pour objectif de créer de nouvelles structures améliorées. La recherche a été menée en essayant de maintenir les propriétés structurelles souhaitées, ce qui justifie l'utilisation d'une telle solution en premier lieu, mais également en considérant son utilisation potentielle comme plate-forme pour la mise en place d’inserts de matériaux périodiques résonants. Ces noyaux cellulaires ont été fabriqués en utilisant la technique du Kirigami (qui est une variante de l'Origami) : il s’agit d’une ancienne technique japonaise qui consiste à créer des structures 3D en pliant et en découpant une feuille de matériau 2D. Cette technique de fabrication peut être utilisée comme un moyen systématique de produire des configurations générales en nid d'abeilles avec des composites à fibres longues par thermoformage et / ou autoclavage. Le principal indicateur utilisé ici afin d’évaluer les performances vibroacoustiques des topologies innovantes proposées est le nombre et la plage de bandes d'arrêt, également connues sous le nom de bandes interdites, qui décrivent les plages de fréquences dans lesquelles les ondes élastiques ne peuvent pas se propager dans la structure. Ce manuscrit est organisé en cinq chapitres. Le premier consiste en un bref aperçu des structures périodiques dans les différents domaines d'ingénierie. L'accent est mis sur les panneaux sandwich et leurs techniques de fabrication les plus populaires sera également décrit. Le deuxième chapitre présentera au lecteur le concept de propagation des ondes élastiques dans les milieux périodiques. De plus, des phénomènes comme les interférences de Bragg ou les bandes interdites résonantes seront présentés ainsi que la théorie de Floquet-Bloch appliquée aux structures à périodiques typiquement utilisées dans l’aéronautique. Cette dernière dérivation mathématique sera fusionnée avec l'approche d'analyse par éléments finis et mise en œuvre comme base pour les outils de prédiction numérique spécialement développés afin de permettre la réalisation d’investigations paramétriques sur des panneaux sandwich complets ou des cœurs nus. La théorie de Floquet-Bloch permet de récolter des informations cruciales sur le comportement dynamique de l’ensemble de la structure en n’effectuant l’analyse que sur une petite partie de celle-ci (cellule unitaire).[...]Honeycomb sandwich panels are well known to provide interesting static out of plane properties because of their high equivalent stiffness whilst containing mass and for this reason, they are widely used as a ‘building brick’ in the Aerospace, Automotive and Naval industries. The environment in which these materials operate involve external forces which excites them in the mid-low frequency range. However, while a high stiffness/mass ratio is a desirable static property, the vibration frequency domain is usually in the high range and therefore they become poor mechanical and acoustic insulators within the frequency range they are usually subjected to. The question addressed then is simple: how periodic concepts can improve the broadband vibroacoustic signatures and performances of those structures? Most of vibroacoustic solutions are frequency band limited, specific and usually include the addition of mass, which for certain engineering segments is disadvantageous. Including vibroacoustic design rules at early stage of product development is one of the main research targets to improve their performance and would allow to design tuned structures without any later intervention or mass increment. This work focuses on investigating existing sandwich panel core topologies and attempt to create novel improved structures. The research was carried out trying to maintain the desired structural properties which justifies the usage of such solution in the first place but also considering its potential use as a platform for Multiphysics resonating periodic material inserts. Such cellular cores were manufactured using Kirigami, which is a variation of Origami, an ancient Japanese technique that consists in creating 3D structures by folding a 2D sheet of material. This manufacturing technique can be used as a systematic way to produce general honeycomb configurations with off-the-shelf long fibre composites by thermoforming and/or autoclaving. The main indicator on which I will focus to evaluate the vibroacoustic performance of the proposed innovative topologies will be the number and range of stopbands, also known as a bandgaps, which describe the frequency ranges in which elastic waves are not transmitted within the structure, in combination with the constituent material and its damping properties. This manuscript is organised in five chapters. The first one consists of a brief overview on periodic structures in the various engineering domains. Emphasis on Sandwich panels and their most popular manufacturing techniques will also be described. The second chapter will introduce the reader to the concept of elastic wave propagation in periodic media. Also, phenomena like Bragg or resonant bandgaps will be explained as well as the Floquet-Bloch theory applied to macro-scale structures such as aeronautical cellular cores.[...

Similarity reasoning for local surface analysis and recognition

This thesis addresses the similarity assessment of digital shapes, contributing to the analysis of surface characteristics that are independent of the global shape but are crucial to identify a model as belonging to the same manufacture, the same origin/culture or the same typology (color, common decorations, common feature elements, compatible style elements, etc.). To face this problem, the interpretation of the local surface properties is crucial. We go beyond the retrieval of models or surface patches in a collection of models, facing the recognition of geometric patterns across digital models with different overall shape. To address this challenging problem, the use of both engineered and learning-based descriptions are investigated, building one of the first contributions towards the localization and identification of geometric patterns on digital surfaces. Finally, the recognition of patterns adds a further perspective in the exploration of (large) 3D data collections, especially in the cultural heritage domain. Our work contributes to the definition of methods able to locally characterize the geometric and colorimetric surface decorations. Moreover, we showcase our benchmarking activity carried out in recent years on the identification of geometric features and the retrieval of digital models completely characterized by geometric or colorimetric patterns

Spatiotemporal coordination of signaling at single molecule resolution

Advances in live-cell single-molecule imaging and modeling over the past decade have invited the closer study of biological structure and dynamics at the nanoscale. The higher resolution of these single-molecule experiments results in finely-grained datasets that can feed detailed quantitative models. Likewise, single-molecule models can account for microscopic details such as noise and heterogeneity inherent to diffusional and chemical processes, which are often neglected in models based on bulk concentrations. Examining microscale biological structures at single molecule resolution in living cells has led to new findings, such as the dynamic regulation of nanoscale structure. I cover three topics from the perspective of single molecules. Chapters 1-3 are on modeling the spatiotemporal coordination of both spontaneous and pheromone-guided yeast polarity establishment. Chapter 4 is on computational modeling and analysis for a technique called Binder/Tag, which we applied to study the conformational dynamics of the protein Src kinase in living cells. Chapter 5 is on modeling clustering-mediated activation of immunoreceptors, using the phagocytic receptor FcγRIIA as a prototypical example.Doctor of Philosoph

Optimal guidance and control of heterogeneous swarms for in-orbit self-assembly of large space structures: Algorithms and experiments

Satellite design has been harshly constrained by surviving entry into space though the majority of the satellite's lifetime exists in much calmer conditions. Significant study has recently gone into assembling satellites and space structures in-orbit. Several methods have been proposed involving an assembler robot or astronaut which puts the parts together, but in the interest of saving resources we believe that it is advantageous to make this process autonomous and robust by leveraging existing optimal guidance and control schemes for a self-assembling swarm. This approach avoids single-point failures, requires significantly less ground support, provides increased reliability due to redundancy, increased flexibility, the ability to reconfigure for future missions, and the ability to self-repair. Since the satellites required could be mass-produced from a small set of different component types, the benefit from economy of scale would reduce the overall mission cost when compared to monolithic satellites. This dissertation details an optimal guidance and control scheme to enable in-orbit self-assembly of a large structure from a heterogeneous swarm of satellites. In the proposed scheme, the component satellites for the heterogeneous swarm are chosen to promote flexibility in final shape inspired by crystal structures and Islamic tile art. After the ideal fundamental building blocks are selected, basic nanosatellite-class satellite designs are presented to enable accurate attitude control simulations. The Swarm Orbital Construction Algorithm (SOCA) is a guidance and control algorithm that allows for the limited type heterogeneity and docking ability required for in-orbit assembly. The algorithm was tested in a simulated perturbed 6-DOF spacecraft dynamic environment for planar and out-of-plane final structures. The algorithm is then experimentally validated coarsely on omnidirectional wheeled robots and precisely on-board the M-STAR robots in the precision flat floor facility in the Caltech Aerospace Robotics and Control lab, the largest of its kind at any university. In support of this effort, a better way of handling nonlinear dynamics constraints within sequential convex programs was developed. SCP is a useful tool in obtaining real-time solutions to direct optimal control, but it is unable to adequately model nonlinear dynamics due to the linearization and discretization required. As nonlinear program solvers are not yet functioning in real-time, a tool is needed to bridge the gap between satisfying the nonlinear dynamics and completing execution fast enough to be useful. Two methods are proposed, sequential convex programming with nonlinear dynamics correction (SCPn) and modified SCPn (M-SCPn), which mixes SCP and SCPn to reduce runtime and improve algorithmic robustness. Both methods are proven to generate optimal state and control trajectories that satisfy the nonlinear dynamics. Simulations are presented to validate the efficacy of the methods as compared to SCP. In addition, several autonomous rendezvous and docking (AR&D) technologies were studied because in-orbit self-assembly requires repeated, reliable autonomous docking to ensure success. Docking small satellites in space is a high-risk operation due to the uncertainty in relative position and orientation and the lack of mature docking technologies. This is particularly true for missions that involve multiple docking and undocking procedures like swarm-based construction and reconfiguration. A tether-based docking system was evaluated in simulation as compared to traditional propulsive methods. The tether-based method provides a way to reduce the risk of the dock, since the docking maneuver is performed with a much smaller satellite and the reeling maneuver can be done gently. Tether-based methods still require some actuation on the docking end of the tether, and propulsion on such small systems is inexact. An electromagnetic docking system was investigated to address these issues. Designed with reconfigurable self-assembly in mind, the gripping mechanism is androgynous, able to dock at a variety of relative orientations, and tolerant of small misalignments. The electromagnetic system can be used either on the end of a tether or on the main spacecraft itself since the electromagnet is well controlled and the measurement of the ambient electromagnetic field can be used as to improve the intersatellite distance estimate enough to reduce the risk of docking to the main spacecraft. The performance of this system was validated experimentally on-board the M-STARs. The performance of the electromagnetic docking system on-board the simulators is then compared against a propulsive docking system tested in the same way. Overall, this dissertation provides optimal guidance and control algorithms for nonlinear systems to enable in-orbit self-assembly of heterogeneous swarms

Determination of World's Humid Tropical Deforestation Rates during the 1990's. Methodology and Results of the TREES-II Research Programme.

Abstract not availableJRC.H-Institute for environment and sustainability (Ispra

Modelling, Simulation and Data Analysis in Acoustical Problems

Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years

Procedures for the analysis and use of multiple view angle image data

It is recognised that the majority of vegetative cover types have anisotropic reflectance characteristics that are largely a function of their canopy geometry. Several studies have made attempts at formulating methods for the use of data remotely sensed from off-nadir directions. The best of these methods attempt to utilise the "extra" information implicitly contained in off-nadir image datasets. In this study, an attempt is made to extract information concerning agro-physical parameters of a number of vegetative cover types using imagery acquired by an airborne sensor, the Daedalus Airborne Thematic Mapper (ATM). It is also recognised in the literature that the nature of spatial variance in images is related to the size and distribution of the objects in the scene and the sampling characteristics of the sensor. In previous work this relationship has been explored by examining scenes using images of varying spatial resolutions, using a number of measurements of spatial variance. The underlying trend of these measurements is then used to interpret the nature of the objects in the scene. No previous work exists which attempts to utilise the change in variance of images acquired at different off-nadir view angles. In this study, the understanding of this relationship is developed by examining the change in variance of a number of vegetative cover types from multiple view angle image datasets. The geometry of the ATM sensor is derived to allow an understanding of the sampling characteristics of the instrument. Two important geometric factors are established: first, the area of the ground resolution element increases with view angle, which effectively reduces spatial resolution at off-nadir angles; and second, overlap between adjacent ground resolution elements increases with view angle, increasing the spatial auto-correlation between these samples. The effects of illumination, atmosphere and topography can all influence variance in an image. A parametric procedure for normalising multiple view angle (and therefore multitemporal) datasets for these factors is developed, based upon the production of reflectance images using a sky radiance model of the spectral and spatial distributions of irradiance, ground measurements of irradiance, and a digital terrain model of the study site. Finally, it is shown that image variance is likely to decrease at off-nadir view angles, the magnitude of this decrease being related to the sensor geometry and (more importantly) the geometry of the canopy. By a simple statistical analytical procedure it is possible to construct broad classes within which the nature of the canopy can be classified